Abstract: Apparatus and methods are provided for encrypting and decrypting information having a header portion and a body portion. The decrypting method includes the steps of reading a current month from a clock, extracting an odd/even month indication from the header portion, generating a first key based on the current month if the odd/even indication is odd and the current month is odd or if the odd/even indication is even and the current month is even, otherwise generating the first key based on a month previous to the current month read from the clock if the odd/even indication is odd and the current month is even or if the odd/even indication is even and the current month is odd, and using the first key for decrypting the encrypted body portion to generate a decrypted body portion.
Abstract: Apparatus and methods are provided for inserting data into a vertical blanking interval (VBI) line of video frames. The method includes the steps of inserting first data into a first vertical blanking interval VBI line for a plurality of consecutive video frames, inserting second data into a second vertical blanking interval VBI line for a plurality of consecutive video frames, counting a number of consecutive video frames having first data inserted into the first vertical blanking interval VBI line, terminating the insertion of first data for a first number of video frames before again inserting first data into the first vertical blanking VBI interval line when the counted number of consecutive video frames into which first data is inserted into the first vertical blanking interval VBI line equals a second number, and repeating the steps.
Type:
Grant
Filed:
June 24, 1994
Date of Patent:
August 6, 1996
Assignee:
Index Systems, Inc.
Inventors:
Henry C. Yuen, Daniel S. Kwoh, Wing P. Leung, Tony T. Tam